This invention relates to the field of controlling and positioning a workpiece in a manufacturing environment. For explanation purposes, the manufacturing process known as induction hardening will be used to aid in the comprehension of the invention. The use of this example is not meant to limit the scope of the background or of the invention to induction hardening, but rather to aid in the understanding of the invention. The proposed invention may be useful in other fields and endeavors as well, such as machining, milling, assembly and so on.
In the hardening process, the surface layers of the workpiece are heated to about 1000 degrees centigrade, and upon quenching, the surface layer is transformed to the martensitic phase. Martensite provides high surface hardness and enhanced resistance to fatigue. Induction hardening is typically used to harden gear teeth, shafts, splines, housings, hubs, yokes and so on. Currently, there are a variety of methods and equipment available for positioning and controlling production work pieces for induction hardening. These methods are commonly called scan induction hardening, pop-up induction hardening and lift and index induction hardening.
Scan hardening is one of the most popular means for induction hardening of steel. It is done to enhance specific properties of the material that include such things as strength, fatigue resistance, and wear resistance. In scan hardening, the workpiece to be hardened is held between centers that are mounted on an “L” shaped cantilever. The induction coil is typically a single turn, or part of a turn, of a heavy section of copper conductor that surrounds the workpiece, incorporating water passages for cooling, and is supplied by a low voltage, high frequency, alternating current. Usually, the coil remains stationary and the workpiece is moved through the center of the coil during hardening. It is, however, quite possible for the coil to be moved and for the workpiece to remain stationary. Where the workpiece is circular in cross-section, the workpiece is usually rotated as it passes through the coil so as to distribute the hardening uniformly around the periphery which might otherwise be uneven due to small asymmetries of heating caused by coil construction or small irregularities in the quench ring. As electrical current is applied to the coil, the workpiece is heated up to the desired temperature. As the workpiece passes through the coil, a quenching fluid is applied to the heated workpiece and hardening occurs. This type of system is somewhat flexible with respect to workpiece length and, to some extend, outside diameter. Induction scanners can vary scanning speed and power, which control the amount of heat applied to different areas of the workpiece. Depending upon the workflow of work pieces, an induction scan hardening system can be vertical, horizontal or at an angle. Vertical scanners are the most common.
Once the workpiece is heated and quenched, the “L” shaped cantilever is returned to its home position so that the workpiece can be removed and the next workpiece put in for processing. The raising and lowering of the workpiece on the cantilever is accomplished by moving the cantilever with either an electrical-mechanical device, such as a servo-motor and drive gears or pulleys, or through the use of hydraulics. The rotation is typically accomplished with an electrical-servo mechanism. This type of scanning is reasonably precise, but is limited in its weight capacity due to the use of the cantilever mechanism and the forces applied to the lifting mechanism.
Another method for induction hardening is called pop-up induction hardening. A workpiece is held in place with a fixture designed to hold the workpiece, instead of centers, although centers could be utilized. The workpiece is then moved into place, popped up, into position with the induction coil. The induction coil then heats the entire surface to the desired temperature, the workpiece is quenched, and then the fixture drops back down to its home position for workpiece removal and the positioning of a new workpiece. A similar method for large work pieces is to place the workpiece in a stationary fixture and have the induction coil move into the proper position prior to heating and quenching the workpiece. This can be done in a vertical, horizontal or angular position and with either electrical-servo mechanism, pneumatics or with hydraulics.
A third method for induction hardening is called the lift and index induction hardening method. This is typically used for complex shapes such as gears, splined shafts or inside splined shafts where it is desired to harden the gear tooth surface or the splined shaft surfaces. There are other uses as well. In this process, the workpiece is held by either centers or a fixture. Typically, in a vertical machine, the workpiece is raised vertically into position next to the inductor. The inductor then moves in horizontally between two teeth or splines. The tooth surface or spline is then heated to the desired temperature and quenched. The induction coil then backs away from the gear tooth or spline and the gear or spline is then rotated or indexed to the next tooth to be hardened. This process continues until all of the teeth have been heated to the desired temperature and quenched. The workpiece is then returned to the home position for removal. This can be done in the vertical, horizontal or angular position through the use of either electrical-servo mechanisms or with hydraulics.
The current methods have some limitations to them. First and foremost is that each of the methods described above are separate and distinct induction hardening processes. By this, we mean that the method for scan induction hardening does not provide for a means to lift and index. Similarly, the means for lifting and indexing does not provide for a continuous scan of a workpiece. Neither of these induction hardening processes provide for a means to do “Pop Up” induction hardening.
Secondly, the existing methods utilize a table or “L” shaped cantilever for positioning the workpiece. This significantly reduces the weight bearing capacity of the induction heating device due to the forces and loading on the cantilever. The current solution to this is to simply build a larger machine for heavier work pieces. This solution costs more and occupies an additional amount of floor space.
Thirdly, in the lift and index induction hardening process, once the workpiece is in position, the inductor must be moved in and out of position to allow for the workpiece to be rotated in order for the next tooth to be aligned with the induction coil. The induction coils are typically much larger and heavier that the production work pieces, which causes greater wear on the equipment and on the accuracy of positioning the induction coil.